The present invention relates generally to part conveyors and more particularly to an accumulating power roll conveyor system.
Many traditional conveyor systems employ a series of modular sections divided into multiple zones that are independently powered. These systems typically use programmable logic controllers, also known as PLCs, to control energization of the different zones based on optical, photo electric or proximity switch sensing of parts within the zones. Examples of such systems are disclosed in U.S. Pat. No. 6,021,888 entitled xe2x80x9cConveyor System and Its Control Methodxe2x80x9d which issued to Itoh et al. on Feb. 8, 2000, and U.S. Pat. No. 5,086,910 entitled xe2x80x9cZone Controlled Conveyance Systemxe2x80x9d which issued to Terpstra on Feb. 11, 1992; both of these patents are incorporated by reference herein. Programmable logic controllers, however, are often expensive and time-consuming to program. U.S. Pat. No. 5,285,887 entitled xe2x80x9cAccumulating Conveyor and Control Systemxe2x80x9d which issued to Hall on Feb. 15, 1994, also discloses a complicated electrical controller and photo electric cell sensor arrangement; this patent is incorporated by reference herein. This construction also suffers from conventional cost, set up and maintenance disadvantages.
Conventional accumulating conveyor systems allow for compression of downstream items or parts on the conveyor. This often occurs when there is only a single stop at the end of the conveyor line and the parts are allowed to stack up or bump into each other until the previous downstream part is removed. Part compression may lead to part removal or operation difficulties since upstream contacting parts are often disturbed when the downstream part is moved. Part damage may also occur at the contact points when the parts are in compression. Moreover, U.S. Pat. No. 5,228,558 entitled xe2x80x9cControl System for an Accumulating Conveyorxe2x80x9d which issued to Hall on Jul. 20, 1993, provides a system that allows for limited compression of the parts by accelerating, decelerating, and stalling drive rollers on the conveyor line, however, part contact can still occur. This patent is also incorporated by reference herein. Finally, it is known to use an escapement mechanism to block and separate parts on a traditional power roll conveyor for a non-zone construction.
In accordance with the present invention, a conveyor for transporting parts includes a first electrical switch, a second electrical switch and an automatically movable stop. In another aspect of the present invention, an accumulating power roll conveyor system has two or more independently driven zones. Yet another aspect of the present invention provides for a part physically contacting against and actuating a switch as the part is located in a zone corresponding with the switch. A further aspect of the present invention provides three electrical switches connected to three independently energizable actuators, three automatically movable stops and an electrical circuit that does not employ a programmable logic controller. In still another aspect of the present invention, a control system for an accumulating power roll conveyor uses optical sensor switches and independently powered zones, but does not employ a programmable logic controller. A method of operating an accumulating power roll conveyor system is also provided.
The accumulating power roll conveyor system of the present invention is advantageous over conventional systems in that one embodiment of the present invention provides a precise physical stop for parts moving in each zone. This allows for stoppage of part movement in a predetermined location in each zone for subsequent operations on the part and to also prevent undesired compression and contact between adjacent parts on the conveyor line. The present invention is further advantageous by employing an analog electrical circuit rather than the more expensive and difficult to set up, programmable logic controller. In one embodiment of the present invention, the physically contacted switches of the present invention conveyor advantageously reduce the labor and part cost traditionally associated with optical and photo electric sensor switches. Furthermore, the zone driving arrangement of the present invention allows for less expensive and more efficient energy consumption, reduced part-to-part contact, and reduced wear and tear on the actuator system. Moreover, in one embodiment of the present invention, the system advantageously achieves destacking or stripping of adjacent parts if more than one part is inadvertently moving in a single zone. Additional advantages and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.